Architecture for electric machine

ABSTRACT

The invention includes an electric machine having a rotor, stator and at least one winding in the stator adapted to conduct a current, and a secondary winding, electrically isolated from the first winding and inductively coupled to the first winding, which may be used to control at least one of the output voltage and current of the first winding.

RELATED APPLICATION

[0001] This application is a continuation application of U.S. Ser. No.10/444,952 filed May 27, 2003.

TECHNICAL FIELD

[0002] The invention relates to electric machines such as alternatorsand motors and, more particularly, to a novel architecture for suchmachines.

BACKGROUND OF THE ART

[0003] Referring to FIG. 1, a typical permanent magnet (PM) machineaccording to the prior art is shown at 100. Prior art PM machine 100 hasa rotor 102, with permanent magnets 104 mounted thereto by a retainingring 106, which is mounted on a rotatable shaft 108. Rotor 102 isadjacent a stator 110 having a plurality of windings 112 interspersedbetween a plurality of teeth 114 mounted to a back iron 116. (For easeof illustration, the adjacent elements of windings 112 in FIG. 1b areshown unconnected.) As is well understood, PM machine 100 may operate ina generator/alternator mode or a motor mode. When operated in agenerator/alternator mode, an external torque source forces rotation ofthe shaft (and thus the rotor and the magnets), and the interaction ofthe magnets and the windings causes a magnetic flux to loop the windingsin the slots. As the rotor rotates, the magnetic flux in the statorstructure changes, and this changing flux results in generation ofvoltage in the windings, which results in an output current that can beused to power electrical devices, or be stored for later use. Whenoperated in a motor mode, a voltage from an external source is appliedto the stator windings which causes current flow in the windings andresults in a magnetic flux to be set up in the magnetic circuit formedby the teeth and back iron. When current is supplied in an appropriatemanner to the windings, the rotor can be made to rotate and thus produceusable torque. The operation of such machines is thus well understood.

[0004] Such PM machines can have an “inside rotor” configuration asshown in FIGS. 1a and 1 b, or an “outside rotor” configuration as shownin FIGS. 2a and 2 b. The reference numerals in FIGS. 2a and 2 bcorrespond to the corresponding features described with reference toFIGS. 1a and 1 b. In the “outside rotor” configuration, however, rotoryoke 108′ replaces rotor shaft 108. For ease of illustration, theadjacent elements of the windings in FIG. 2b are also shown unconnected.

[0005] Irrespective of whether operated in an alternator or motor mode,the magnetic flux path in these prior art PM machines is as partiallyand simply depicted in FIG. 3, the flux path as indicated by the arrows118, and the poles and virtual poles denoted by an “N” or an “S”. It isthis magnetic flux 118 which induces a voltage in the alternator winding112 (or in the case of a motor, creates the magnetic attraction with thepermanent magnet 106 to cause rotor rotation), as described above.

[0006] Prior art PM machines (and particularly PM alternators) sufferfrom at least two limitations which has limited their usefulnesssomewhat, namely: (1) the output of the PM alternator may only becontrolled within the machine (i.e. varied) by varying the rotor speed(assuming a fixed geometry machine), and (2) if a short circuit or otherinternal fault occurs in the machine, the internal fault current canbecome extremely destructive to the machine, particularly in high powerapplications. With reference to the first drawback, this intrinsicfeature particularly limits the usefulness of a PM generator incircumstances where the rotor rotation speed cannot be independentlycontrolled. It would therefore be desirable to improve thecontrollability of PM machines, generally.

[0007] PM machines offer certain attractive advantages for use in highspeed applications, and particularly as an integrated starter-generator(ISG) for a propulsive or prime-mover gas turbine engine, in which thePM machine is mounted directly to a turbine shaft of the engine. Thisshaft, of course, is driven at whatever speed is required for therunning of the gas turbine engine (typically anywhere in the range of0-50,000 rpm) and thus the shaft speed cannot be varied to suit thecontrollability limitations of the PM machine, but rather is dictated bythe mechanical output requirements of the engine. Therefore, althoughthe ISG designer will know the average steady state speed of the turbineshaft at cruise, can thus design an PM alternator system to providesufficient electrical output necessary to power the aircraft systems atcruise (where the engine typically spends most of its operation cycle),accommodations must be made for take-off (where the turbine shaft may beturning at twice cruise speed, doubling alternator output) and landingapproach (where turbine shaft speed may half of cruise speed, halvingalternator output). The problem is an order of magnitude greater forcertain military applications, where cruise speed is rarely maintainedfor any length of time. The prior art therefore poses optimizationproblems to the ISG designer, where critical over-power and under-powerscenarios must be managed to achieve a satisfactory design.

[0008] There are other drawbacks inherent prior art designs, whichresult in complicated mechanisms and fabrication techniques. U.S. Pat.No. 6,525,504 to Nygren et al. shows one example of a relativelycomplicated solution to the control of certain aspects of the operationof a PM machine used in high voltage power generator applications. Thedevice offers only limited control over operation of the machine, andits complexity makes it unsuitable for higher reliability and lighterweight applications such as, for example, aircraft applications.

[0009] Accordingly, there is a need to provide an improved PM machinewhich addresses these and other limitations of the prior art, and it isan object of this invention to do so.

SUMMARY OF THE INVENTION

[0010] In one aspect, the present invention provides an electric machineoperable as an alternator, the machine comprising a magnetic rotormounted for rotation about an axis; a stator adjacent the rotor, thestator including a plurality of radial slots defined in the statorbetween pairs of teeth, and a bridge mounted to the stator in at leastone of the slots and extending between a pair of said teeth defining theat least one slot, the bridge dividing the at least one slot into atleast two slot portions; a first winding forming at least a portion of afirst circuit, the first circuit adapted to deliver generatedelectricity from the machine, the first winding having a loop portionincluding at least a first leg and a second leg, the loop portiondisposed in the at least one slot such that the first leg is disposed ina first one of said at least two slot portions and adjacent a first sideof the bridge, and the second leg is disposed in a second of said atleast two slot portions and adjacent a second side of the bridge, thefirst and second sides of the bridge opposing one another; and a secondwinding forming at least a portion of a second circuit, the secondcircuit electrically isolated from the first circuit, the second windingdisposed in the stator adjacent the second leg of the first winding.

[0011] In another aspect, the invention provides an electric machineoperable as an alternator, the machine comprising: a rotatable magneticrotor; and a stator assembly mounted adjacent the rotor assembly, thestator assembly including a plurality of openings including a firstopening and a second opening, the first and second openings beingseparated by a portion of the stator assembly, a first electricalwinding electrically connected to a first circuit, the first circuitadapted to provide electricity output from the machine when the machineis operated as an alternator, the first electrical winding disposed atleast partially in the first opening and at least partially in thesecond opening so as to at least partially form a loop, and a secondelectrical winding connected to a second circuit, the second electricalwinding electrically isolated from the first electrical winding, thesecond winding disposed in the second opening adjacent the firstwinding, wherein said portion of the stator assembly defines a portionof at least two magnetic circuit paths in the stator assembly forguiding magnetic flux generated as a result of the rotor rotating aboutthe stator, and wherein a first one of said at least two magneticcircuit paths at least partially encircles the first opening and firstwinding therein, and wherein a second one of said at least two magneticcircuits at least partially encircles the second opening and the firstand second windings therein, and wherein the secondary magnetic circuitis defined entirely within the stator assembly.

[0012] In another aspect, the invention provides a machine operable asan alternator, the machine comprising: a rotatable rotor; at least afirst winding electrically connected to a machine output adapted todeliver generated output electricity from the machine when the machineis operated as an alternator; at least a second winding including acurrent-limiting device, the second winding electrically isolated fromthe first; and a stator adjacent the rotor, the stator defining at leasta first opening and a second opening, the first winding disposed in thefirst opening and second opening, the second winding disposed only inthe second opening, the stator and rotor together defining a primarymagnetic circuit path around the first opening, whereby relativemovement between the rotor and the stator causes a primary magnetic fluxto flow around the primary magnetic circuit path which thereby induces avoltage across the first winding and an associated current flow in thefirst winding, the stator also defining a secondary magnetic circuitwithin the stator around the second opening, the first and secondwindings being disposed in the first and second openings and the firstand second openings being positioned in the stator such that, in use,said voltage and current induced in the first winding induces asecondary voltage and an associated current flow in the second winding,wherein the current-limiting device is adapted to prevent a current flowin the secondary winding when a pre-selected threshold current in thesecondary winding is exceeded, the second winding thereby limiting amaximum current flow in the first winding to at least a desired maximumcurrent flow limit.

[0013] In another aspect, the invention provides a machine operable asan alternator, the machine comprising: a rotor having a plurality ofmagnetic poles; a first winding electrically connected to a machineoutput, the output adapted to deliver generated output electricity fromthe machine; a second winding including a current-limiting device; and astator adjacent the rotor, the first and second windings disposed in thestator, the stator and rotor together defining a first magnetic circuitaround a portion of the first winding, the stator defining a secondmagnetic circuit within the stator around a portion of the first andsecond windings, wherein the first and second windings are inductivelycoupled such that, in use, a voltage and current induced in the firstwinding by rotation of the rotor induces a secondary voltage and acurrent flow in the second winding, and wherein when a pre-selectedthreshold current is exceeded in the second winding, thecurrent-limiting device prevents current flowing through the secondarywinding, thereby limiting a maximum current flow in the first winding.

[0014] In another aspect, the invention provides a permanent magnetmachine operable as an alternator, the machine comprising: a rotorhaving a plurality of permanent magnetic poles; a stator adjacent therotor, the stator including at least a first winding disposed in atleast one slot in the stator and a transformer disposed in the stator,the first winding inductively coupled to the rotor such that rotation ofthe rotor induces an output voltage and current in the first winding,the transformer electrically connected to the first winding and adaptedto control at least one of said output voltage and current of the firstwinding.

[0015] In another aspect, the invention provides an electric machineoperable as an alternator, the machine comprising: a stator; a magneticrotor opposing the stator; and at least two windings disposed in thestator and electrically isolated from one another, wherein a first ofthe at least two windings comprises a primary winding in the stator forat least one of producing and consuming power, and wherein rotation ofthe rotor induces an output voltage and current in the primary winding,and wherein a second of the at least two windings comprises a secondarywinding in the stator, the secondary winding being arranged and disposedin the stator adjacent a portion of the primary winding such that saidinduced current in the primary winding induces at least a voltage acrossthe secondary winding, and wherein the secondary winding is inductivelycoupled substantially only to the primary winding and is inductivelyisolated from the rotor, and wherein the electric machine furtherincludes means for controlling current flow in the secondary winding,said means adapted to thereby affect current flow in the primarywinding.

[0016] In another aspect, the invention provides an electric machineoperable as an alternator, the machine comprising: a rotor having aplurality of magnetic poles; a stator adjacent the rotor, the statorhaving an electromagnetic core portion defining a plurality of radiallyextending teeth, at least one bridge portion extending between twoadjacent teeth, a first winding wound around the core and wound aroundthe at least one bridge portion, and a second winding electricallyisolated from the first winding and disposed in the stator adjacent thefirst winding, the second winding wrapped around the core portion butdisposed remote from the bridge portion.

[0017] In another aspect, the invention provides a method of controllingan alternator, the alternator having a stator having at least one coreportion extending between a plurality of radial teeth, a first windingwound around the at least one core portion and a second winding adjacenta portion of the first winding, the first and second windingselectrically isolated from one another, the method comprising the stepsof rotating the rotor to induce primary current, the primary currentthereby inducing a secondary current in the second winding, andcontrolling the current flow in the second winding to thereby limit themaximum current in the first winding.

[0018] In another aspect, the invention provides a method of controllinga permanent magnet alternator, the alternator having a rotor, stator andat least one winding in the stator adapted to conduct an output currentinduced in the winding by rotation of the rotor, the method comprisingthe steps of: providing secondary winding electrically isolated from theat least one winding; placing the secondary winding adjacent a portionof the at least one winding; inductively coupling the secondary windingto the at least one winding and inductively isolating the secondarywinding from the rotor, such that in use the at least one windinginduces at least a voltage in the secondary winding; and using thesecondary winding to control at least one of the voltage and current ofthe at least one winding.

[0019] Still other inventions are disclosed in this specification andattached figures, as well.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For a better understanding of the present invention and to showmore clearly how it may be carried into effect, reference will now bemade by way of example to the accompanying drawings, showing articlesmade according to preferred embodiments of the present invention, inwhich:

[0021]FIG. 1a is a cross-sectional view of a typical permanent magnet(PM) machine according to the prior art;

[0022]FIG. 1b is an exploded isometric view of the prior art device ofFIG. 1a;

[0023]FIG. 2a is a cross-sectional view of a typical PM machineaccording to the prior art having an “outside rotor” configuration;

[0024]FIG. 2b is an exploded isometric view of the prior art device ofFIG. 2a;

[0025]FIG. 3 is a cross-sectional view similar to FIG. 1a, schematicallyshowing magnetic flux paths;

[0026]FIG. 4a is a cross-sectional view of a PM machine according to thepresent invention;

[0027]FIG. 4b is an exploded isometric view of the device of FIG. 4a;

[0028]FIG. 4c is a rear isometric view of a portion (i.e. a few adjacentloops) of the primary winding of the device of FIG. 4a;

[0029]FIG. 4d is an isometric view of the secondary winding of thedevice of FIG. 4a;

[0030]FIG. 4e is an enlarged isometric view of a portion of the rotorand stator of the device of FIG. 4a, with a portion broken away toreveal detail therein and schematically showing some magnetic flux pathsin the device;

[0031]FIG. 5a is an exploded isometric view of a second embodiment of aPM machine according to the present invention, with the stator shown inghost lines to reveal the winding detail therein;

[0032]FIG. 5b is an enlarged isometric view of a portion of the statorof the device of FIG. 5a, with a portion broken away to reveal detailtherein;

[0033]FIG. 5c is an enlarged cross-sectional partial view of the deviceof FIG. 5a, schematically showing magnetic flux paths in the device;

[0034]FIG. 6a is an exploded isometric view of a third embodiment of aPM machine according to the present invention;

[0035]FIG. 6b is an isometric view of the stator of the device of FIG.6a;

[0036]FIG. 6c is a rear isometric view of the stator of FIG. 6b;

[0037]FIG. 6d is an enlarged isometric view of a portion of the rotorand stator of the device of FIG. 6a, with a portion broken away toreveal detail therein;

[0038]FIG. 6e is a partial cross-sectional view of the portion of therotor and stator shown in FIG. 6d;

[0039]FIG. 6f is a cross-sectional view along the lines 6 f-6 f in FIG.6e;

[0040]FIG. 7a is an isometric schematic representation of a method formaking primary windings in accordance with the present invention;

[0041]FIG. 7b is much-enlarged cross-section of a portion of a statorshowing the windings of FIG. 7a;

[0042]FIG. 8a is an enlarged isometric view and a cross-sectional viewsimilar to FIGS. 6d and 6 e, respectively, schematically representingelectrical and magnetic activity on start up of the present invention;

[0043]FIG. 8b is an enlarged isometric view and a cross-sectional viewsimilar to FIG. 8a, respectively, schematically representing electricaland magnetic activity immediately after the moment in time representedin FIG. 8a;

[0044]FIG. 9 is a schematic of an equivalent electrical circuit of onephase the device of FIG. 6a;

[0045]FIG. 10 is a schematic of an embodiment of a secondary windingcontrol circuit;

[0046]FIG. 11a and 11 b are schematics of other examples of secondarywinding control circuits;

[0047]FIG. 12a is an enlarged isometric view and a cross-sectional viewsimilar to FIGS. 6d and 6 e, respectively, schematically representingelectrical and magnetic activity of another embodiment of the presentinvention employing a low Curie point material;

[0048]FIG. 12b is an enlarged isometric view and a cross-sectional viewsimilar to FIGS. 6d and 6 e, respectively, schematically representingelectrical and magnetic activity after the secondary winding fuse of thepresent invention blows;

[0049]FIG. 13a is an enlarged isometric cross-sectional view of aportion of the stator of another embodiment of the present invention;

[0050]FIG. 13b is an enlarged isometric cross-sectional view of aportion of the stator of an alternate design for the embodiment of FIG.13a;

[0051]FIG. 14 is a schematic of an aircraft accessory system employing amulti-channel version of the present invention; and

[0052]FIG. 15 shows a gas turbine engine incorporating the presentinvention, with a portion of the engine broken away to reveal across-section thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] A permanent magnet (PM) machine according to the presentinvention is depicted in at 10 in FIGS. 4a to 4 f. Referring first toFIGS. 4a and 4 b, PM machine 10 has a rotor 12 which includes aplurality of permanent magnets 14 retained by a yoke 16 and retentionsleeve portion 18. Machine 10 also has a stator 20 which includes atleast a primary winding 22 and at least a secondary winding 24 (forclarity, only one of each such winding is shown), separated in thisembodiment by a winding air gap 26 and disposed in radial slots 28between a plurality of adjacent teeth 30 in a back iron 32. (For ease ofillustration in FIG. 4b, the adjacent elements of secondary winding 24are shown unconnected.) The winding air gap serves as insulation and maybe replaced by other suitable insulation. A rotor air gap 34 separatesrotor 12 and stator 20 in a typical fashion, and a stator tooth gap 36separates adjacent teeth 30 at a rotor interface surface 38 of stator20. Primary winding 22 and secondary winding 24 are thus electricallyisolated from one another. Stator 20 also includes a core or “bridge”portion 40 bridging adjacent pairs of teeth 30 and passing betweenadjacent portions of primary winding 22, as will be described in moredetail below.

[0054] The materials for PM machine 10 may be any deemed suitable by thedesigner. Materials preferred by the inventor are: samarium cobaltpermanent magnets, maraging steel (preferably 250 or 300) retentionsleeve, aluminum yoke, copper primary and secondary windings, a suitableelectromagnetic material for the stator teeth and for the back iron.

[0055] Referring to FIGS. 4c and 4 e, primary winding 22 of theembodiment of FIG. 4a consists of a conductor which enters a first end27 of a slot 28 a on a first side 40′ of bridge 40, and a first legportion 23′ of winding 22 travels down slot 28 a, an end turn portion23″ of winding 22 crosses bridge 40 at the second (i.e. other) end 29 ofslot 28 a and a second leg portion 23′″ travels back along slot 28 a andexits slot 28 a from the first end 27, but on a second side 40″ ofbridge 40 (i.e. opposite to the first side 40′ the winding entered).Primary winding 22 then continues along the first end 27 of the statorto the next appropriate slot 28 b and again enters from the first end 27of slot 28 b, but preferably from the second side 40″ of bridge 40 (i.e.the same side of bridge 40 as it exited the last slot 28 a). Primarywinding 22 then travels down slot 28 b, loops around bridge 40 at thesecond end 29 of slot 28 b, then proceeds back up slot 28 b and exitsthe first end 27 of slot 28 b, and is now again on the first side 40′the bridge piece, and so on. Primary winding 22 is thus positioned inthe desired slots 28 in stator 20. This particular pattern bothfacilitates assembly (as will be discussed further below) and providesan orderly arrangement for primary winding 22, and also beneficiallyassists winding separation within PM machine 10 9see FIG. 7b).

[0056] Referring to FIG. 4d, secondary winding 24 in the embodiment ofFIGS. 4a-4 f is a shorted winding to provide a squirrel cageconfiguration. Secondary winding 24 thus has a plurality of legs 42extending between end rings 44.

[0057] Referring to FIG. 4e, a close-up partial isometric section showsthe relative arrangements of primary winding 22 and secondary winding 24(only a portion of one primary winding 22 is shown for clarity). Inoperation, as will be described in greater detail below, the interactionof magnets 14 and windings 22, and windings 22 and 24, creates magneticflux within PM machine 10. Referring to FIG. 4e, a primary magnetic fluxpath or magnetic circuit 46 and a secondary magnetic flux path or magnetcircuit 48 are set up within PM machine 10, as are representedschematically in FIG. 4e. The secondary magnetic flux path is isolatedfrom the rotor and rotor magnetic circuit.

[0058] Primary magnetic circuit 46 includes rotor 12, rotor air gap 24,bridge 40 and the portion of stator teeth 30 between rotor 12 and bridge40. Primary magnetic circuit encircles primary winding 22 and, in use(as described further below) either causes or is caused by a currentflow in primary winding 22, depending on whether machine 10 is operatedas an alternator/generator or motor, respectively. Secondary magneticcircuit 48 includes bridge 40, back iron 32 and the portion of statorteeth 30 between back iron 32 and bridge 40. Secondary magnetic circuitencircles secondary winding 24. Secondary winding 24, as will bedescribed further below, is provided for control purposes andpreferably, therefore, not connected to an output circuit of machine 10.

[0059] Referring again to FIG. 4a, stator 20, bridge 40 and slot 28together define two slots or openings 28′ and 28″, with one opening 28′for the primary winding only, and another opening 28″ for the primaryand secondary windings. The primary magnetic circuit encircles opening28′ while the secondary magnetic circuit encircles opening 28″. In FIG.4a, the opening 28′ is radially closer to the rotor than the otheropening 28″. Within the slot 28, bridge 40 extends a portion of thedistance from the radially innermost portion of slot 28 to the radiallyoutermost portion of slot 28 to thereby define openings 28′ and 28″. Thedesigner will select the size of the bridge, as well as the rest of thestator dimensions, based at least in part on the desired properties ofthe magnetic circuits in the machine to yield the desired machineperformance, etc. Referring to FIG. 4e, bridge 40 also preferablyextends the entire distance from stator faces 27 to 29 and thus isadjacent the primary winding 22 along the length of legs 22 a and 22 c.Leg 23′ is preferably substantially parallel to winding 24 along its leg25′ extending the length of opening 28″.

[0060] Referring to FIGS. 5a-5 c, a second “inside rotor” embodiment ofthe present invention is shown. The same reference numerals are used todenote the analogous elements described with reference to FIGS. 4a-4 d.The skilled reader will also appreciate the relative similarities anddifferences in construction and operation of typical “outside” vs.“inside” rotor configurations, and thus these will not be discussedfurther here. Aspects of the second embodiment not specificallydescribed below may otherwise be assumed to be made in accordance withthe description of the analogous element described above.

[0061] Referring to FIGS. 5a and 5 b, the second embodiment of thepresent invention is another multi-winding, multi-phase configuration.In other words, there are multiple primary windings 22 and secondarywindings 24, preferably one for each phase. For clarity, only one phaseis depicted. Though only the windings of one phase will be describedbelow, preferably the description will apply to the windings of allphases.

[0062] Referring first to FIG. 5a, each phase of primary winding 22consists of a conductor which, in a manner similar to that describedabove, enters a first end 27 of a slot 28 a on a first side 40′ ofbridge 40, travels down slot 28 a, crosses bridge 40 at the second (i.e.other) end 29 of slot 28 a and travels back along slot 28 a and exitsslot 28 a from the first end 27, but on a second side 40″ of bridge 40(i.e. opposite to the first side the winding entered). Primary winding22 then continues along the first end 27 of the stator to the nextappropriate slot 28 b and again enters from the first end 27 of slot 28b, but preferably from the second side 40″ of bridge 40 (i.e. the sameside of bridge 40 as it exited the last slot 28 a). Primary winding 22then travels down slot 28 b, loops around bridge 40 at the second end 29of slot 28 b, then proceeds back up slot 28 b and exits the first end 27of slot 28 b, and is now again on the first side 40′ the bridge piece,and so on. Primary winding 22 is thus positioned in the desired slots 28in stator 20.

[0063] In this embodiment, each phase of secondary winding 24 consistsof a conductor which enters one end 27 of the slot 28 a occupied by theprimary winding 22 of that phase and then exits slot 28s from theopposite end 29 and continues to the next appropriate slot 28 b(preferably the next slot occupied by this phase of primary winding 22,as depicted in FIG. 5a), and so on.

[0064] Referring to FIG. 5b, the relative arrangements of primarywinding 22, secondary winding 24 and bridge 40 can be seen within stator20. Referring to FIG. 5c, a schematic representation of the primary andsecondary magnetic circuits flux paths 46 and 48, respectively, is shownwhen PM machine 10 is in use.

[0065] A third embodiment of the present invention is disclosed in FIGS.6a-6 f. Referring first to FIGS. 6a & 6 c, this embodiment is anoutside-rotor, 3-phase, dual “channel” PM machine, depicted with one set(i.e. “channel”) of primary windings 22 absent (for clarity), as will bedescribed in more detail below. The same reference numerals are used inFIGS. 6a-6 f to denote the analogous elements described with referenceto the embodiments above, and thus these elements will not beredundantly described here but rather addressed only as required.Aspects of the third embodiment which are not specifically describedbelow may be assumed therefore to be otherwise made in accordance withthe description of the analogous elements above.

[0066] As mentioned briefly above, and for reasons which will becomemore apparent below, in this embodiment, stator 20 of PM machine 10 isconceptually divided into an “a” half and a “b” half, and thus windings22 and 24 will be described in terms of primary windings “22 a” and “22b” and secondary windings “24 a” and “24 b”. Other features associatedwith windings 22 and 24 may also be described as “a” or “b” specific.Primary windings 22 b are not depicted in FIGS. 6a-6 c for clarity, butmay be assumed to be otherwise identical to primary windings 22 a.

[0067] Referring to FIG. 6a, in this embodiment three primary windings22 a are provided, namely primary windings 22 a ¹, 22 a ² and 22 a ³, toprovide the desired 3-phase configuration. Each primary winding 22 a isprovided with its own primary terminal 50 a (see FIG. 6b) for ease ofconnection to an associated primary circuit (not shown). Secondarywindings 24 a and 24 b each have squirrel cage-type arrangement (i.e.with legs 42 and end rings 44) and have secondary terminals 52 a and 5b, respectively, for ease of connection to an associated secondarycircuit. Referring to FIGS. 6d and 6 e, preferably (as will be describedin greater detail below) each leg 42 of secondary windings 24 includes acurrent-limiting device such as a fuse or breaker element 54. Stator 20has a plurality of passages 58 defined on its inner periphery to act asan oil transfer mechanism, as will also be described in more detailbelow. Referring again to FIG. 6a, preferably paper spacers 56 areplaced between primary windings 22 and stator 20, and between secondarywinding 24 and stator 20, for insulation purposes.

[0068] Bridges 40 are preferably non-integral with stator 20, and thusinserted as an assembly as depicted schematically in FIG. 6c, whichadvantageously permits the designer to select different materials forbridge 40 and stator 20. For example, a bridge material may be chosen toalter the magnetic or performance characteristics of machine 10, as willbe discussed in greater detail below. Non-integral bridges 40 may alsobeneficially facilitate machine assembly, as explained further below.

[0069] Referring in particular to FIGS. 6a-6 c, as mentioned thisembodiment has a “multi-channel” architecture, in that a plurality offully independent “sets” of primary and secondary windings are provided.In this case, two such sets are provided (i.e. sets “a” and “b”described briefly above), namely primary windings 22 a and 22 b (primarywinding 22 b is not shown, for clarity) and secondary windings 24 a and22 b. This multi-channel architecture permits a plurality ofmotor/alternators to exist within the same stator, and which may eitherbe operated conjunctively, or independently, as desired. For example, innormal machine operation, the outputs of the winding sets may becombined to provide a single output, but in the event of a fault whichrequires one winding set to be shut down, the remaining winding set(s)may continue operation unaffected. This feature thus permits more thanone motor/generator to exist within the same machine (as is discussed ingreater detail below), thereby providing redundancy which may veryvaluable in applications where a complete shutdown would becatastrophic.

[0070] Stator 20 has a tooth gap 36 preferably provided in accordancewith the applicant's co-pending application Ser. No. 10/393,252, filedMar. 21, 2003, the contents of which are incorporated into thisdisclosure by reference. Though not shown specifically in thisdisclosure, but as incorporated by reference from the applicant's saidco-pending application, tooth gap 36 is not necessary in the stator faceadjacent the rotor (i.e. near 28 a, as in FIG. 4e), but rather slots 28may open to the opposing face (i.e. the face opposing the stator's‘rotor face’-i.e. nearer to 28 b in FIG. 4e) or slots 28 may have nosuch openings adjacent either 28 a or 28 b, but rather having openingsonly at faces 27 and 29.

[0071] Primary windings 22 and secondary winding 24 are preferably eachcomposed of single conductor provided in a single turn configuration.This single conductor, single turn configuration is preferred because itreduces the probability of a short circuit within the winding. Primarywindings 22 are preferably stamped or otherwise provided from sheetmetal and then pre-bent into a desired shape prior to insertion into thestator. An example series of fabrication steps are shown schematicallyin FIG. 7a. Advantageously, bridge 40 may be inserted into the windingsbefore insertion into the stator, and this removable bridge portion andstator architecture permits the windings to be completely pre-assembledbefore being inserted into the stator, thereby improvingmanufacturability. Referring to FIG. 7b, primary windings 22 are alsopreferably installed in stator 20 such that they are individuallyradially separated from one another to provide increased anti-shortcircuit protection between adjacent windings.

[0072] Referring to FIGS. 6c and 6 d, in this embodiment wherein bridges40 are non-integral with stator 20, primary windings 22 may be“pre-wrapped” around bridges 40 prior to assembly into teeth 30 ofstator 20. When a whole-number of turns around bridge 40 are made byprimary winding 22 (in this case, one turn is made), primary winding 22enters and exits slot 28 of stator 20 between from the same side, asdescribed above. This design feature advantageously permits primarywindings 22 to be pre-assembled with bridges 40 (and spacers 56, asdesired) prior to insertion into slots 28 of stator 20. This permitstraditional winding machines (and their associated manufacturing andtolerance difficulties) to be avoided altogether in the present design.

[0073] Referring to FIG. 8a, in use, whether in a motor or alternatormode, the interaction of magnets and primary winding 22 causes a primaryflux path 46 to be set up which runs down a first portion (i.e. theupper end) of tooth 30, across bridge 40, and back up a correspondingfirst portion of an adjacent tooth 30, and then to and through the rotorto complete the loop, as depicted by the solid arrows in FIG. 8a. Thisprimary flux path causes (or is the result of, depending on whether PMmachine is operated as a motor or an alternator) current to pass throughprimary winding 22 (in a closed primary circuit). Referring to FIG. 8b,this current flow through primary winding 22 causes a secondary fluxpath 48 to be set up through a second portion (i.e. the lower end) ofteeth 30, through back iron 32, back up through the corresponding secondportion of an adjacent tooth 30 and then back through bridge 40 to closethe secondary loop. This secondary magnetic circuit causes a secondarycurrent to flow through secondary winding 24 (in a closed secondarycircuit)

[0074] The magnetic flux in secondary path 48 thus loops the portion ofsecondary winding 24 opposite primary flux path 46, and the interactionof primary winding 22 and secondary winding 24 thus sets up a secondarymagnetic circuit in machine 10. It can clearly be seen, therefore, thatthe magnetic flux path(s) of the present invention are entirelydifferent than is present in a typical prior art PM machine. As will bedescribed in greater detail below, these characteristics of the presentinvention present many advantages to a PM machine designer.

[0075] When used as an alternator, a PM machine will generate voltageand current which may be used as required, or stored for later use.Often, a conditioning step of some description is required to convertthe raw output of the alternator into a more useful form (typically byvarying the voltage, current and/or frequency and perhaps also rectifythe output into DC current). As discussed in the Background, in a gasturbine integral-starter generator (ISG) application, in normaloperation in an alternator mode, variations in engine speed and loadresults in an ISG output current and voltage which requires conditioningbefore the generated electricity is useable by on-board aircraft systemssuch as electric oil pumps, fuel pumps and other accessories. Therefore,means may be provided outside PM machine 10 to control and condition themachine output (i.e. preferably the output of primary winding 22).

[0076] However, when operated as an alternator, the present inventionalso permits the output the primary winding(s) 22 to be controlled to acertain extent through a manipulation of at least the current secondarywinding(s) 24, as will now be described.

[0077] Referring again to FIGS. 8a and 8 b, it will be appreciated that,in essence, the present invention set ups a transformer-typerelationship between primary winding 22 and secondary winding 24, as isschematically represented FIG. 9 by an simple equivalent circuit. In thepreferred embodiments depicted in FIGS. 4a to 6 f, the equivalent“transformer” is a 1:1 transformer, i.e. the number of turns in primarywinding 22 equals the number of turns in secondary winding 24 (here,each has only one turn). In such a “transformer”, the followingrelationship exists between the primary and secondary windings:

I _(PRIMARY) *V _(PRIMARY) =I _(SECONDARY) *V _(SECONDARY)

[0078] Thus, the magnetic flux developed within secondary magneticcircuit is proportional to the current flow in primary winding(s) 22 andinversely proportional to the magnetic coupling within secondarymagnetic circuit. The magnetic flux in secondary magnetic circuit isproportional to the magnetic coupling, and inversely proportional to thecurrent flow in secondary winding 24 (i.e. the current induced in thesecondary winding causes the secondary flux to be cancelled). Therefore,the current flowing in secondary winding 24 directly influences thecurrent generated in the primary winding 22 by the rotating magneticsystem of PM machine 10, and the current flow is a function of thecurrent flow in the primary windings. The secondary windings 24 areinductively coupled only to the primary winding 24 (excluding leakage,etc.), and thus the secondary winding 24 and secondary magnetic circuit48 are only influenced by the flux in the primary magnetic circuit 46set up by the primary winding 24 (except in the case of a low Curiepoint bridge, of the type describe further below, when the bridge is ator exceeds the bridge material's Curie point temperature).

[0079] This aspect of the present invention permits the designer to usethe secondary winding to manipulate the output of primary winding 22,and thus secondary winding 24 may be used as a source of control PMmachine 10. Means for controlling the operation of PM machine are thusavailable within the machine itself, as the “control” current may begenerated within PM machine 10, that is in secondary winding 24. In someinstances, therefore, no external source of control current may berequired. The novel architecture of the present invention thereforelends itself to many novel possibilities for control systems for themachine, a few examples of which will now described.

[0080] In one example control scheme, the output (i.e. from a primarywinding 22) of PM machine 10 in an alternator mode may be controlled bymechanical means by directly influencing the current in the secondarywinding 24. Referring again to FIGS. 6d and 6 e, a current limitingdevice 54, such as a fuse element, is preferably provided in one or morelegs 42 (preferably all legs) of secondary winding 24. Referring toFIGS. 8a and 8 b, as mentioned, current in secondary winding 24 is afunction of current in the primary winding 22. Thus, as current in theprimary winding rises (such as in the case of an internal fault such asa short circuit) so, too, will the current in the secondary winding.Referring to FIG. 12b, in use, when the current in secondary winding 24exceeds a certain threshold, a fuse element 54 would “blow”, therebycreating an open-circuit in secondary winding (i.e. no secondarycurrent) and, by reason of the electrical inter-relationship between theprimary and secondary circuits, the output current of primary circuitwill be limited. With no current flow in the secondary winding, the fluxin primary magnetic circuit 46 induces in a significant flux insecondary magnetic circuit 48. Consequently inductive reactance isincreased, which can be used limit maximum output current to a maximumsynchronous impedance of machine 10. (Prior to opening of the fuse, whensecondary current is allowed to flow in the secondary winding, theresulting secondary flux is in the opposing direction and thus tends tocancel the secondary flux. Hence, the operation of machine 10 isrelatively unaffected by the presence of the secondary until thesecondary circuit opens.) This permits the control of the machine'simpedance and offers PM machine 10 intrinsic thermal protection againsta short-circuit in primary winding 22 when operating in an alternatormode. Any suitable fuse may be used.

[0081] Prior to opening of fuse 54 (i.e. in normal machine operation),secondary winding 24 as disclosed in the embodiment of FIGS. 6a-6 foperates in a simple short-circuited squirrel cage arrangement, and thuswill have no perceptible effect on primary winding 22. In other words,when secondary winding 24 is fully short circuited, PM machine 10 maybeoperated in a manner substantially in similar to prior art machines.

[0082] In a second example control scheme, current in the secondarywinding 24 can be influenced by electronic means to control the currentin primary winding 22. Direct electronic control of current in secondarywinding 24 can be achieved by an impedance or other control system, suchas the examples depicted in FIGS. 10, 11a and 11 b which provideproportional type or other control adjustments of the current insecondary winding 24, to thereby control the current in primary winding22.

[0083]FIG. 10 shows an example of a simple arrangement for solid statesecondary winding electronic control circuit 60 for control secondarywinding 24 for machine 10. The main elements are D_(I) Bridge rectifier,and Q_(I) IGBT device (Insulated Gate Bipolar Transistor). The deviceQ_(I) could also be substituted by another type of device, such as apower MOSFET or other switching device. In this example, multiplesecondary windings 24 ¹, 24 ², 24 ³ (e.g. as in the example of amultiphase machine having a secondary winding for each phase) preferablyeach have similar circuits, e.g. as 60 is depicted in FIG. 10, whichcould be controlled by a single control system. V_(sI), the controlvoltage, is used to switch Q_(I) ‘on’ or ‘off’ and, as such, may be usedto control the average DC current flow in the D_(I) rectifier bridgeand, consequently, the AC current flow in secondary winding 24. In thisarrangement, secondary winding 24 preferably has multiple turns(relative to primary winding 22) such that the current being switched bythe Q_(I) device would be stepped-down to only a fraction of the currentflow in primary main winding 22 to thereby permit low current controlcircuitry connected to secondary winding 24 to control a high currentmachine output from primary winding 22. (The switched voltage at Q_(I)would generally still be higher than the primary machine voltage, but itwill be understood that this is still practical since Q_(I) devices areavailable which operate at over 1500V). This control arrangement isuseful as a voltage regulator when the output of machine 10 (i.e. theoutput of primary winding 22) is to be rectified for use as a DC supplyor further conditioned as desired. In use, the current induced in thesecondary is affected and controlled by the elements in the secondarycircuit, and this control permits the current and/or voltage of theprimary to be affected as desired to control the operation and behaviourof PM machine 10.

[0084] Many other control schemes are also possible. Referring FIG. 11a,a different secondary winding electronic control circuit 60 is shown, inwhich the output of secondary winding 24 fed in parallel throughparallel diode 62 and transistor 64 pairs (in this case the transistorsare NJFETs) to permit the secondary current to be modulated to thuscontrol the primary winding 22 output. Referring to FIG. 11b, a secondembodiment of a secondary winding control circuit 70 is shown, in whichthe output of secondary winding 24 fed to a thermally-sensitive switch72. Still other control schemes are possible, as will be appreciated byone skilled in the art upon consideration of this disclosure.

[0085] In a third example control scheme, the current in secondarywinding 24 can be influenced by varying the magnetic coupling in thesecondary magnetic circuit to thereby control the primary windingcurrent. For example, referring again to the figures the configurationand material selection for components such as stator teeth 30, back iron32 and bridge 40 will also vary the magnetic properties of the secondarymagnetic circuit, thus permitting the designer to “control” theperformance of PM machine 10. In one example, described further below,the secondary magnetic circuit includes a low Curie point material suchas ferrite, when the machine operates with the secondary magneticcircuit at or above the Curie temperature the effect or influence of thesecondary winding would be greatly reduced.

[0086] As discussed above, non-integral bridge pieces 40 may providebenefits for the assembly of PM machine 10. Also, as briefly mentioned,the provision of a non-integral bridge permits the designer to select adifferent material for bridge 40. For example, additional short-circuitcontrol can be provided to PM machine 10 in accordance with theteachings of the applicant's U.S. Pat. No. 6,313,560 (the '560 patent),the contents of which are incorporated by reference into thisdisclosure. The '560 patent teaches that materials with a low Curietemperature (referred to as low Curie point materials in thisdescription), such as ferrite, can be beneficially used in electricmachines to provide thermal protection in the event that a fault causesnormal operating temperatures to be exceeded. This concept may also beapplied in the present invention, as will now be described.

[0087] Referring again to FIGS. 6a-6 f, preferably bridges 40 are madeof different material than teeth 30, which thereby permits the designerto alter the behaviour of the primary and secondary magnetic circuits.Most preferably, bridge 40 is made of a low Curie point material of thetype described in the '560 patent, such as ferrite.

[0088] Referring now to FIG. 12a, in use, in such a thermally-protectedembodiment primary winding 22 is preferably closely thermally coupled tobridge 40 pieces to permit a fast and effective control of the machinein the fault condition. In the event of a fault that raises thetemperature of a bridge 40 to or above the Curie point of the ferritebridge material, bridge 40 begins to lose its ability to conductmagnetic flux, and thus (eventually, as temperature increases) becomes“invisible” to the magnetic circuit in stator 30. The primary andsecondary magnet circuits are thus joined into one circuit (reference47), as magnetic flux (eventually) no longer crosses bridge 40, or fluxis at least greatly reduced.

[0089] In fact, preferably, the low Curie point material is selectedsuch that when the Curie point of bridge 40 is reached, bridge 40doesn't completely stop magnetic flux from passing therethrough (andthus doesn't completely “shut down” the primary current down, but ratheras the Curie point is reached and exceeded, the amount of magnet fluxpassing though the bridge is progressively reduced, thereby acting justto “turn down” the primary current, rather than shut it off completely.The amount the current is “turned down” by bridge 40 is controlled bythe amount of magnetic “short circuit” experienced as a result ofreaching the bridge material Curie temperature, and is thus affected notonly by bridge 40 material, but also by (a) tooth pitch, (b) back ironthickness, (c) tooth length, and (d) back iron material, among otherthings. The designer may use this knowledge to control the “turn down”behaviour of PM machine 10 in the event a machine fault occurs.

[0090] To enhance the effectiveness of a low Curie point embodiment ofthe present invention, a close thermal coupling between the windings andthe low Curie point material of bridge 40 is advantageous and thuspreferred. This close coupling may be achieved by close contact betweenprimary winding 22 and bridge 40, and/or may be enhanced by the use ofbonding material between the windings and the low Curie point material.

[0091] Advantageously, the use of a low Curie point bridge material canprovide thermal protection to PM machine 10 in fault situations wherethe current in secondary winding 24 is not high enough, for example, toblow a fuse 54 and yet continued operation of machine 10 could result indamage to the machine. Thus, the use of a low Curie point material inconjunction with the present invention can permit intrinsicallyredundant safety systems to be incorporated.

[0092] Another significant advantage of PM machine 10 is that, when alow Curie point material is employed as described, if the internal faultis a short in a loop (or loops) of the winding, the described low Curiepoint embodiment can permit only the faulty loop(s) to be shut down orturned down, leaving the operation of the rest of the windingessentially unaffected. The bridge and stator arrangement, inconjunction with the independent ferrite bridge portions, in effectforms a plurality of serially-connected by otherwise independentalternators within PM machine 10.

[0093] A low Curie point material may also be used in the secondarycircuit for control purposes. For example, if a low Curie point material(such as ferrite) were used in the secondary magnetic circuit of thepresent invention, for example in the back iron, the design could permitthe current in the primary circuit to be increased as the low Curiepoint material in the secondary circuit is heated above its Curietemperature. This may be a beneficial feature, depending on theperformance criteria or specification for a particular application forPM machine 10. For example, this feature may be used to increase outputto a cooling system such that the machine, operated as an alternator,both provides cooling power and controls temperature.

[0094] Referring to FIG. 13a and 13 b, the present invention may beprovided including a cooling system including a coolant 80 (preferablyoil) within PM machine 10. Oil is circulated through passages 58 insidea stator jacket 82 around and along the primary and secondary windingsto assist in cooling them. In FIG. 13b, an oil jet 84 in an insert 86directs oil onto the end turn of the primary winding. If the insert 86is made of aluminum or copper, the stray inductance of the end turn isalso reduced, thereby reducing the overall machine impedance.

[0095] Accordingly, control schemes such as those disclosed above may beemployed individually or may be combined as desired to permit severalcontrol features to exist contemporaneously within the PM machine. Asprior art fixed-geometry PM machines typically are not controllable inany way other than by the speed at which they are operated, thiscontrollability feature of the present invention is of significant valueto the PM machine designer, particularly in those applications where therotational speed of the machine cannot itself be used to control machineoutput. The present invention also offers a robust and reliable designsuitable for aerospace applications.

[0096] In essence, the present invention provides a type of internalcurrent-limiting transformer (in the described embodiments, a 1:1transformer, but other ratios are possible) built into the magneticstructure of the machine. The “primary” is connected electrically inseries with the main output feeders of the alternator, and the“secondary” is configured preferably as a short circuit, which willbecome an open circuit, by means of a fuse, or other circuitinterrupting or current limiting means, above a certain pre-selectedtemperature. Typically, the pre-selected threshold temperature will bethe maximum safe sustained operating temperature of the machine, abovewhich the machine is susceptible to thermal damage (e.g., say about 300°C. when typical electric machine construction materials are used). Whenthe secondary becomes open circuit, current flow in the primary issignificantly reduced as a result of the inductive reactance of the“transformer” under no load conditions, which thereby results in anincrease in the machine impedance. Preferably, the increase in machineimpedance is a significant one (e.g. doubling the machine impedance),such that the short circuit current in the primary is effectivelylimited to a value equal to the maximum power rating of the machine. Theadvantage of using this “transformer” type arrangement is that eachstator slot may be protected by its own “transformer-breaker”, and thusthe voltage that is being fused is only a fraction (e.g. ⅙^(th) in adual-channel 3 phase machine of the type described further below) of thetotal generated voltage. Consequently, the breaker/fuse in the secondarywill be less likely to experience an arc when the circuit is opened.

[0097] The ‘transformer’ of the present invention may also be remotefrom the stator, such that a portion of the primary and some or all ofthe secondary are disposed external to the stator.

[0098] The net effect of the low Curie point embodiment described aboveis that two thermal protection schemes may be implemented in themachine, namely (1) a low Curie point type over-temperature protectionscheme, which provides intrinsic and automatic reversible (i.e.non-permanent) overload protection to prevent permanent damage to themachine for moderate to severe temperature overloads, and (2) a hightemperature protection scheme which will automatically react in theevent that (i) the first-mentioned mechanism does not sufficientlycontrol the short circuit current within the time desired, and/or (ii)in situations where the short circuit resistance(s) in the machine is(are) very low.

[0099] As discussed above, the present invention also includes a“multi-channel” design which can, among other things, offer inherentredundancy useful in aerospace applications. Referring to FIG. 14, a PMmachine 10 of the type described with reference to FIGS. 6a-6 f above inessence provides a single rotor rotating relative to multiple (in thedescribed case, two) independent stators. Thus, rotor 12 rotatesrelative to a “virtual” stator 20 a (the portion with primary windings22 a) and also relative to a “virtual” stator 20 b (the portion withprimary windings 22 b). This, PM machine is “two-in-one machine in thiscase. The output of these two “machines” may then be combined, whichpermits the option of operating the “two machines” as one. PM machine 10is then preferably connected to fully redundant accessory systems, whichmay include redundant power conditioning units (PCU) 90, oil pumps 92,fuel pumps 94, hydraulic pumps 96 and other electrically-run accessories98. In an gas turbine ISG application, this dual- or multi-channeldesign permits a fully redundant system (system A+system B, in FIG. 14)to provided with a minimum of hardware, thereby minimizing weight andspace and increasing reliability. As well, since generator efficiency isproportional to I² losses, it is often preferable to run two “machines”like this, each at ½ of the output current, rather than one machine afull output current. Further, power from the two “machines” may beshared, if desired, between the PCUs with the appropriate connections,etc., to permit redundancy in the case of a “machine” or PCU failure.

[0100] The present invention is particularly well suited, among otherthings, to prevent overheating problems of an internally short circuitedpermanent magnet arrangement that is driven continuously, such as in thecase of an internal fault in a machine 10 driven by a shaft ‘S’ in gasturbine engine ‘GT’, as depicted in FIG. 15. The invention also permitsa certain level of control to be attained over an alternator which isdriven at variable speeds (i.e. driven by an operating propulsiveaircraft gas turbine).

[0101] The above description is meant to be exemplary only, and oneskilled in the art will recognize and changes may be made to theembodiments described without departing from the scope of the inventiondisclosed. For example, the machine may be single or multi-phase, singleor multi-channel. The windings may have single or multi turns per slot,the number of turns of primary windings does not have to equal thenumber of turns of secondary winding, the number of turns of a windingnot necessarily have to be a whole number, the number of primarywindings does not have to equal the number of secondary windings, as oneor more windings in a slot may perhaps be present in a slot. A varietyof winding types may be used (squirrel cage, lap, etc.), and thewindings may be any conductor(s) (i.e. single conductor, more than onewire, insulated, laminated, etc.) or may be superconductors. Inmultiphase machine, there may be zigzag, delta, or Y-connected windingsin accordance with known techniques. There need not be an air gapbetween the primary and secondary winding, as long as the windings areelectrically isolated from one another.

[0102] The rotor can be electromagnetic (i.e. permanent magnet notnecessary), and may be provided in an outside or inside configuration,or any other suitable configuration. The bridge may be provided in oneor more slots, and may be integral or non-integral with the rest of thestator. A secondary bridge may also be provided, in the form of the backiron, for example, if the secondary winding(s) are wound around the backiron. Other secondary bridge configurations are also possible.

[0103] Secondary winding may also be used for control purposes in motormode. Other portions of the stator and rotor, such as back iron forexample, may be provided of a low Curie point material to achieve thebenefits of the present invention. Still other modifications which fallwithin the scope of the present invention will be apparent to thoseskilled in the art, in light of a review of this disclosure, and suchmodifications are intended to fall within the equivalents accorded tothe appended claims. In this application, it is to be understood thatthe term ‘alternator’ is used generically to mean a device used forcreating electricity, and is not intended therefore to be limited to adevice for generating an output alternating current.

1-36 (Deleted)
 37. A method of making an electric machine, comprisingthe steps of: providing a rotor having an axis of rotation; providing astator for coaxial mounting with the rotor to provide a radial gaptherebetween, the stator having a pair of end faces and a plurality ofslots extending between the end faces; providing an integral winding inthe plurality of slots, including bending the winding into apredetermined shape and inserting the winding into the plurality ofslots substantially through one of said end faces.
 37. The methodaccording to claim 1 wherein a multi-piece stator is provided, andwherein a portion of the stator is inserted into intermediate bentportions of the winding prior to inserting the winding and said statorportions into said slots.
 38. The method according to claim 1 whereinthe winding is provided from sheet metal
 39. The method according toclaim 1 wherein winding material is self-supporting when bent into shape40. The method according to claim 1 wherein the method further comprisesproviding a plurality of said windings according to said method, andwherein each of said winding represents a single phase
 41. The methodaccording to claim 1 wherein the plurality of said windings are insertedsubstantially simultaneously into the stator
 42. The method according toclaim 1 wherein the plurality of said windings are individually radiallyseparated from one another in the stator relative to the rotor axis. 43.An electric machine comprising: a rotor having an axis of rotation; astator coaxially mounted with the rotor to provide a radial gaptherebetween, the stator having a pair of end faces and at least a firstset of slots defined axially in the stator and extending between the endfaces; an integrally continuous winding successively passing through theset of slots, wherein the winding enters and exits each slot from one ofsaid end faces; and wherein the stator further comprises a bridgeassembly disposed within the stator, and wherein the winding loopsaround the bridge assembly.
 44. The electric machine according to claim43 wherein the bridge assembly is disposed within the slots.
 45. Theelectric machine according to claim 43 wherein the winding is selfsupporting relative to the stator.
 46. The electric machine according toclaim 43 wherein the windings are adapted for axial insertion into thestator, and wherein the bridge assembly is adapted for insertion intothe windings prior to said insertion of the windings.